Hutch’s workshop tips
Hutch has a rather stubborn Enfield cylinder head to remove
Ihave a 1951 Enfield G2 Bullet in the workshop for a bit of resurrection. The history of the bike is that it was apparently taken off the road and stored in large bits around 1954. A new owner had bolted it mostly together and had it running, but a year or so later it has found its way into my workshop. Some of the initial work showed that although it may have only been on the road for its first three or four years it must have had a pretty big paper round in that time!
One of the symptoms it was showing was a lack of compression and a slight “sucking” on the exhaust when turned over. The present owner also told me that the piston had been seized in the barrel and he had managed to free it with some oil and work. I suspected a non-seating exhaust valve at least, so it was time for a closer inspection of the top end internals.
Fortunately, Hitchcocks m/c's (hitchcocksmotorcycles.com) have all the Enfield manuals online to download so I printed out the few relevant paragraphs on removing the head and barrel. Though many people moan about more modern manuals like Haynes (although I grew up with them so there is a feel to them like hearing the shipping forecast), when you try to use some of the manufacturer's manuals for older bikes, it changes your view a bit.
The bike was put on the bench and all the big bits removed to give access to the top end of the motor. Following the manual, all the engine peripheries like oil feed pipes, plug, rocker boxes were removed, bagged and put aside for cleaning later.
I turned the motor over and checked that both pushrods were free to turn when the valve was closed. I had done this before but better to be sure than stripping the top end for want of a simple adjustment. Again, following the manual, the rocker assemblies and the pushrods were removed, making a mental note that the exhaust pushrod was significantly longer than the Inlet.
The six cylinder head nuts were removed, along with the one small base nut and this is where the fun began. Neither the head nor barrel would separate from each other or the crankcases, not even with a little gentle persuasion, heat or the crankcase studs just below the barrel being loosened. That motor had been together for nearly 70 years and was not about to part easily. Sigh…
A little later I decided to try something I have never done before and only seen pictures of; a large amount of string was fed down the plug hole and the engine was turned using the kick-start until the piston compressed the string into the combustion chamber. In theory, as the piston comes up to compression, the head would be ‘encouraged' to release. But the head was still not for moving. Eventually I dropped the primary drive cover off, applied a little more force via the end of the crank with a socket and a long ratchet. Slowly the base gasket showed signs of a bit of movement and edged up. At last.
But my celebration of slightly separating the top end from the bottom end was short-lived. I realised that there was not enough room under the top frame rail to lift the top end off complete over the long barrel/head studs. This one's a fighter!
With the engine at bottom, or inner dead centre I lifted the head and barrel assembly as much as I could. With an extra pair of hands to help, I could eventually remove all the barrel studs (sounds easy when you say it) and lift the top end away from the piston, which itself looked okay but had a broken ring.
With the top end assembly still welded together but on the bench, and the string removed, it was time to interrogate the combustion chamber with a piece of wood and a mallet to separate; not pretty and to no avail in spliting the head from the barrel.
The half-length stud was removed from the barrel, the last remaining one, and heat was applied with a hot air gun/plastic welder. The head was still reluctant to move so it was allowed to cool, heated again (and again) and finally with a little more persuasion the head joint gave up.
It is amazing how well the two surfaces were joined, considering how easily they can blow sometimes.
What was holding it all together? It appeared to be a compound of carbon, gasket and some sort of gasket cement that is probably no longer available on health and safety grounds!
The cylinder barrel looked fine and would come back with a bit of a hone, but obviously new rings were needed. Was the exhaust valve leaking like I'd suspected? With the blunt force I'd had to use on the head with a piece of wood, we'll never know. I thought it better to just drop the valves, decoke, reface and lap them back into the seats. Then it was time to put it all back together again. Old bikes – who says they've all been to bits a million times?